ES2922751T3 - Mapping between codewords and layers in a system that implements HARQ - Google Patents

Abstract

In a transmitter or transceiver, the codewords of the HARQ processes can be mapped or assigned to various layers for the transmission and/or retransmission of information on a radio channel. Exemplary embodiments provide various mappings that facilitate, for example, HARQ processes. For example, a code word can be mapped into a plurality of layers that are equal in number to a channel range of a radio channel to be used for transmission. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Mapping between codewords and layers in a system that implements HARQ

TECHNICAL FIELD

The present invention relates generally to radio communication systems, devices, software and methods and, more particularly, to techniques and mechanisms for mapping between codewords and layers ( codeword to layer mapping) associated therewith.

BACKGROUND OF THE TECHNIQUE

In its beginnings, radiotelephony was designed and used for voice communications. As the consumer electronics industry continued to mature, and processor capabilities increased, more devices became available for use that enabled wireless data transfer between devices, and more applications became available that operated based on on such transferred data. Of particular interest are the Internet and local area networks ( LANs - Local Area Networks). These two innovations allowed multiple users and multiple devices to communicate and exchange data between different devices and device types. With the advent of these devices and these capabilities, users (both business and residential) discovered the need to transmit data and voice from mobile locations.

The infrastructure and networks that support this transfer of voice and data have also evolved. Limited data applications, such as text messaging, were introduced in so-called "2G" systems, such as the Global System for Mobile Communications (GSM). Packet data systems over radio communication became more usable in GSM with the inclusion of General Packet Radio Services (GPRS). 3G systems, and then the even higher bandwidth radio communications introduced by Universal Terrestrial Radio Access (UTRA) standards, made applications such as web browsing more accessible. easily to millions of users (and with a more tolerable delay).

Although new network designs have been released by network manufacturers, future systems are being discussed and developed that offer greater data processing capabilities in end-user devices. For example, the so-called 3GPP - 3rd Generation Partnership Project ( LTE) standardization project is intended to provide a technical basis for radio communications in the coming decades. Among other things to take into account with respect to LTE systems, is that they will allow downlink communications (that is, in which the direction of transmission goes from the network to the mobile terminal) using frequency division multiplexing orthogonal ( OFDM - Orthogonal Frequency Division Multiplexing) as a transmission format and will allow uplink communications (that is, in which the direction of transmission is from the mobile terminal to the network) using a Carrier Frequency Division Multiple Access ( SC-FDMA -Single Carrier Frequency Division Multiple Access).

Modern wireless communication systems specific for packet-based communication often include Hybrid Automatic RepeatreQuest (HARQ) functionality in the physical layer to achieve robustness against radio channel degradation. LTE and Wideband Code Division Multiple Access (WCDMA) are two examples of systems where such functionality is available. The basic idea behind HARQ is to combine Forward Error Correction (FEC) with Automatic Repeat-ReQuest (ARQ), encoding the information contained in the data block and then adding error detection information such as Cyclic Redundancy Check ( CRC). After receipt of the encrypted data block, it is decrypted and the error detection mechanism is used to check whether the decryption is successful or not. If the data block was received without error, an acknowledgment message ( ACK) is sent to the transmitter indicating a successful transmission of the data block and that the receiver is ready for a new data block. On the other hand, if the data block was not decoded correctly, an acknowledgment message is sent. negative acknowledgment ( NACK - negative acknowledgment) which means that the receiver expects a retransmission of the same data block. After receiving the retransmission, the receiver can choose to decode it independently or to use some or all of the previous receptions of the same data block in the decoding process.

The coded bits of the channel that originate from the same block of information bits are generally called a "codeword". This is also the terminology used in the LTE specifications to describe the output directed to a sub-frame. from a single HARQ process that provides a particular transport block and is the result of processing the information bits by performing, for example, turbo encoding, rate matching, interleaving, etc. Another interesting feature of LTE is its support for multiple antennas on both the transmit and receive sides In a multiple transmit antenna device or system, the resulting codewords are then modulated and distributed among the antennas of transmission to perform transmission.The first modulated codeword can be mapped to, for example, the first d The transmit antennas and the second modulated codeword can be mapped to the remaining two transmit antennas in a four transmit antenna system.

Precoding is a popular technique used in conjunction with multi-antenna transmission. The basic principle involved in pre-coding is to mix and distribute the modulation symbols between the antennas while also potentially taking into account current channel conditions. Pre-coding can be implemented by, for example, multiplying the symbol vector carrier information containing modulation symbols by a matrix that is selected to match the channel. Sequences of symbol vectors thus form a set of parallel symbol streams and each of these symbol streams is usually called a "layer" ( "layer1'). Therefore, depending on the selection of the pre-coder in a particular implementation, a layer may directly correspond to a certain antenna or a layer may be distributed, through precoder mapping, among several antennas (also known as antenna ports). The mechanism by which codewords are mapped to particular layers in such systems is called "mapping" or, more specifically, "codeword-to-layer mapping".

In a multi-antenna system (often called a MIMO system), it may be useful to transmit data from several HARQ processes at once, in which case the overall process is also known as multiple codeword transmission. Since the codewords are mapped to the layers, the process can alternatively be called multi-layer transmission. Depending on the conditions of the radio channel, this process can increase data transmission speeds considerably, since under favorable conditions the radio channel can support more or less as many layers as the minimum number of transmit and receive antennas. This means that the channel can support at most the simultaneous transmission of a certain number of codewords, and that particular number depends in turn on the mapping between codewords and layers. In the simplest case, each codeword is mapped to a single layer and so the number of supportable layers obviously equals the number of supportable codewords. One of the most significant characteristics associated with channel conditions in the field of high-speed multi-antenna transmission is the so-called channel rank. The channel range can vary from one to the minimum number of transmitting and receiving antennas. Taking a 4x2 system as an example, that is, a system or device with four transmit antennas and two receive antennas, the maximum channel range is two. The channel range varies in time as fast fading alters the channel coefficients. Generally speaking, the channel range also determines how many layers and ultimately also how many codewords can be successfully transmitted at the same time. Therefore, if for example the channel rank is one at the time of transmission of two codewords that are mapped to two different layers, then there is a high probability that the two signals corresponding to the codewords will interfere so much that they scrambled words will be erroneously detected at the receiver. The number of layers per channel usage (for example, in LTE one channel usage would correspond to a single resource element) that are transmitted simultaneously is sometimes called the transmission range. With pure spatial precoding schemes, such as the spatial multiplexing mode in LTE, the transmission range is equal to the number of layers.

Along with pre-coding, adapting the transmission to the channel range implies the use of as many layers as the channel range indicates. In the simplest of cases, each layer would correspond to a particular antenna. Taking, purely as an example, the current case of four transmission antennas in LTE systems, the maximum number of codewords is limited to two, while up to four layers can be transmitted. For devices or systems that have only two transmit antennas, the mapping is relatively straightforward since the number of layers equals the number of codewords. However, for devices and systems that have, for example, four or more transmit antennas, there are potentially fewer codewords than layers, so the codewords must then be mapped to the layers in some predetermined way. The question then arises as to how to map the codewords to the layers. Various conventional mappings between codewords and layers have been proposed and will be described in more detail below. Although these conventional mappings work well when considering, for example, first time transmission performance, they may not be optimal in other circumstances, for example, when considering the efficiency of the HARQ operation for the rebroadcasts.

Accordingly, it would be desirable to provide other mappings between codewords and layers for systems, methods, devices, and software that avoid the problems and disadvantages described above.

WO 2006/130541 A2 discloses systems and methodologies that facilitate rank reduction (eg of a user device) as a number of transmissions therefrom increases. This rank reduction can improve resistance to interference and make it easier to maintain the code rate despite the spread of transmissions. Additionally, rank reduction information may be encoded together with CQI information to generate a 5-bit CQI signal that may facilitate updating a user rank upon each CQI transmission (eg, approximately every 5 minutes).

SUMMARY

The invention is embodied in accordance with the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:

Figure 1 illustrates an exemplary LTE access network in which exemplary embodiments may be implemented;

Figure 2 represents an example of LTE physical layer information signal processing with which exemplary embodiments can be associated;

Figure 3 shows an example of an antenna mapping function in more detail;

Figures 4(a)-4(d) illustrate a first conventional set of mappings between codewords and layers;

Figures 5(a)-5(d) illustrate a second conventional set of mappings between codewords and layers;

Figures 6(a) and 6(b) illustrate mappings between codewords and layers according to exemplary embodiments;

Figure 7 is an exemplary block diagram of a transmission device in which mappings between codewords and layers may be implemented in accordance with these exemplary embodiments;

Figures 8 and 9 are flowcharts illustrating transmission procedures according to exemplary embodiments;

Figure 10 is an exemplary block diagram of a receiving device in which knowledge of mappings between codewords and layers is used in accordance with these exemplary embodiments; Y

Fig. 11 is a flowchart illustrating a reception procedure according to an exemplary embodiment.

DETAILED DESCRIPTION

The following description of exemplary embodiments of the present invention refers to the accompanying drawings. The same reference numerals in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

To provide a context for the more detailed discussion of mappings between codewords and layers in accordance with these exemplary embodiments, the exemplary radio system illustrated in Figures 1-3 will be considered first. Starting with the nodes and interfaces of the radio access network of Figure 1, it will be seen that this particular example is provided in the context of LTE systems. However, the present invention is not limited in its applicability to transmitters or transmissions associated with LTE systems, and instead may be used in any system in which multiple transmit antennas are employed, including, but not limited to systems, devices and procedures for Wideband Code Division Multiple Access ( WCDMA), GSM, UTRA, E-UTRA (evolved UTRA ), High-Speed Packet Access (HSPA), Ultra Mobile Broadband ( Ultra-Mobile Broadband - UMB), Worldwide Interoperability for Microwave Access (WiMAX) and others. Since, however, the example of Figure 1 is given in terms of LTE, the network node that transmits and receives over the air interface is called an eNodeB, several such eNodeBs 200 being illustrated therein.

In the context of the air interface, each eNodeB 200 is responsible for transmitting signals to and receiving signals from one or more cells 202. Each eNodeB includes multiple antennas, for example, 2, 4, or more transmit antennas, as well as potentially multiple receive antennas, for example, 2, 4, or more receive antennas, and performs functions including, but not limited to, encoding, decoding, modulation, demodulation, interleaving, de-interleaving, etc., with respect to the physical layer of said signals. Note that, as used in this disclosure, the phrase "transmit antennas" is specifically understood to include, and is generic to, physical antennas, virtual antennas, and antenna ports. The eNodeBs 200 are also responsible for many higher functions associated with communications control in the system including, for example, scheduling users, handoff decisions, and the like. The interested reader desiring more information on transmission or reception functions associated with LTE or other systems in which these exemplary embodiments may be deployed is directed to the book entitled "3G Evolution - HSPA and LTE for Mobile Broadband", by Erik Dahlman et al., published by Elsevier Ltd., 2007.

However, consider Figure 2 to briefly discuss the baseband processing associated with downlink transmission of signals (i.e., possibly transferred through the core network 203 to an eNodeB 200 and then into cells 202 to the target mobile terminal(s), eg, EM 204 in FIG. 1). In it, two data transport blocks 300 are being processed for transmission by an eNodeB 200 using spatial multiplexing. In steps 302, cyclic redundancy check (CRC) bits are inserted for use by the receiver to detect errors. In steps 304, channel coding is applied to the transport blocks to provide protection for the payload data against deficiencies presented by the radio channel. The Automatic Hybrid Repeat Request ( HARQ ) steps 306 are performed to extract or repeat a few code bits from the blocks of code bits provided by the channel encoder to generate a precise set of bits to transmit within a time interval. TTI - transmit time interval, for example, based on various criteria such as the number of allocated resource blocks, the selected modulation scheme and the order of spatial multiplexing. This means that the HARQ stages 306 do not necessarily produce the same coded bits for each transmission attempt of the same transport block of information bits. In LTE, the signals corresponding to a TTI are transmitted through a so-called subframe that lasts for 1 ms.

At step 308, the codewords produced by the HARQ block are scrambled (multiplied) by a bit-level mask or masking sequence, which aids in radio signal interference suppression upon reception. The selected data modulation, for example, Quadrature Phase-Shift Keying ( QPSK), 16-state Quadrature Amplitude Modulation ( 16 QAM - Quadrature amplitude modulation with 16 states), or Amplitude Modulation in 64-state quadrature ( 64 QAM), is then applied at step 310 to transform the masked bit blocks into corresponding modulation symbol blocks. These modulation symbols are then mapped to different antennas and/or different antenna ports at step 312. In LTE nomenclature, an antenna port corresponds to the transmission of a particular downlink reference signal that may, or may not, , correspond to a real physical antenna. The symbols to be transmitted on each antenna (1-n in Figure 2, e.g. 2, 4, 8, 16) are then mapped to respective resource blocks 314 and sent for OFDM processing (not shown) before transmission. by the eNodeB 200.

Antenna mapping stage/block 312 is of particular interest in transmission processing for these exemplary embodiments. The antenna mapping process can be further subdivided into mapping the codewords produced by modulation block 310 to the layers and pre-encoding the resulting symbol vectors to generate the antenna (or signal port) mapped symbols. antenna), as shown in Figure 3. An example is provided here with two sets of codewords that are mapped to three layers by the layer mapping function 400. Figure 3 illustrates two symbol vectors v1 and v2 associated with all three layers. These symbol vectors are then pre-encoded by applying one or more pre-encoding matrices by pre-encoding function 402, ie, by matrix multiplication of the pre-encoding matrix(es) by the incoming symbol vectors. A detailed description of precoding is beyond the scope of this discussion. However, it will be appreciated that the illustration of mapping to three layers and four transmit antennas in Figure 3 is purely exemplary, and that these exemplary embodiments are applicable to other numbers of layers and/or transmit antennas. As described above, the selection of the number of layers (i.e. transmission range) will generally vary based on channel range (possibly among other criteria) and the number of antennas may vary from system to system or even between systems. transmission devices within systems.

For any given system, device, or implementation, there will generally be a fixed number of transmit antennas, and thus one or more predetermined codeword-to-layer mappings will generally be available for use in performing the codeword-to-layer mapping. which is illustrated in, for example, Figure 3. This mapping may change during operation of a particular transmitter or device as a function of the given channel range, i.e., codewords may be mapped to more or fewer layers during operation. transmission to another device. Figures 4 and 5 illustrate some conventional sets of mappings between codewords and layers for systems or devices with four transmit antennas. For example, Figures 4(a)-4(d) depict a first conventional set of mappings between codewords and layers. Starting with Figure 4(a), if, for example, the channel conditions have been determined to correspond to a characteristic of transmission range 1, then a single codeword 500 is mapped to a single layer 502. layer 502 is fed into a pre-encoder 504, which pre-encodes the symbols and distributes them among the four transmit antennas 506-512.

For a channel of rank 2, transmission rank 2 is suitable and mapping between codewords and layers can be performed, for example, as shown in Fig. 4(b). In it, two codewords 514 and 516 are mapped to two layers 518 and 520, respectively. These two layers 518 and 520 provide their respective symbol streams to the pre-encoder 504, which in turn pre-encodes the symbols and distributes them among the four transmit antennas 506-512. For a rank 3 channel, one can use transmission range 3, which is illustrated in Figure 4(c) in which a first codeword 522 is mapped to one layer 523, while a second codeword 524 is mapped to two layers 526 and 528 using a 530 serial-to-parallel (S/P) converter. The three resulting layers are then pre-encoded and their symbols are distributed among the four transmit antennas 506-512. For a rank 4 channel, a transmitter can use the mapping between codewords and layers illustrated in Figure 4(d). In it, two codewords 532 and 534 are each mapped to two different layers, i.e. layers 536 and 538 for codeword 532 and layers 540 and 542 for codeword 534 via converters S/P 544 and 546, respectively. The four resulting layers are then pre-encoded by unit 504 and their symbols are distributed among the four transmit antennas 506-512.

Another conventional set of mappings between codewords and layers is illustrated in Figures 5(a)-5(d). In these, the mappings between codewords and layers for ranges 1-3, illustrated in Figures 5(a)-5(c), are the same as those described above for the previous conventional set of mappings of Figures 4( a)-4(c) and are therefore not further described in this disclosure. However, the mapping for a rank 4 channel feature is different. Instead of mapping two codewords each to two different layers (as shown in Figure 4(d)), this conventional set of mappings maps a first codeword 600 to one layer 604 and the second codeword 602 to three layers. different layers 606, 607 and 608 through an S/P unit 610. The resulting layers are then pre-encoded through unit 504 and their symbols are distributed among the four transmit antennas 506-512. This particular mapping has been claimed to be beneficial in increasing the accuracy of the provision of channel quality information from the receiver when employing certain advanced types of receiver employing successive interference cancellation techniques.

The conventional mappings between codewords and layers that have been described above with respect to Figures 4(a)-5(d) work well and incur relatively little performance loss compared to all possible mappings if only the transmission performance the first time. However, if retransmissions are taken into account, eg as part of the HARQ processing described above, then other mappings may be desirable. For example, suppose that at a given time, a transmitter/transceiver determines that the radio channel on which information is being transmitted has a channel rank of four. The transmitter/transceiver then uses, for example, the conventional mapping depicted in Figure 4(d) for the first transmission or initial transmission of a data block, and thus two codewords are mapped to four layers as shown in Figure 4(d). Furthermore, suppose that one or both of the transmitted codewords are subsequently not correctly detected at the receiver, in which case the transmitter is requested to resend the information contained in these two codewords. However, by the time these codewords are retransmitted, the channel has changed its rank, for example, from rank four to rank two, making it generally impossible to successfully transmit two four-layer mapped codewords simultaneously. Thus, the transmitter is required to reduce the transmission range (ie, reduce the number of layers used for transmission) and only transmit single codeword symbols at a time. Taking this into account, the conventional set of mappings between codewords and layers shown in Figures 4(a)-4(d) must, however, use only two codewords in order to use only two layers, that is say, as shown in Figure 4(b).

Therefore, it is not possible, using the conventional predetermined set of mappings provided in Figures 4(a)-4(d), to use two layers for transmission when only single codeword symbols need to be transmitted. Therefore, the transmitter would have to retransmit the code word using only a single layer. A similar problem exists with respect to the conventional set of mappings illustrated in Figures 5(a)-5(d). This, in turn, prevents packet chase combining on the receiving side and also means that retransmissions are limited to half as many bits encoded as the original transmission. For first transmissions with high encoding rates, this can represent a substantial loss of encoding gain.

The problem described above with respect to the conventional mappings between codewords and layers of Figures 4(a)-5(d) can have a significant impact on the efficiency of the HARQ operation. For example, using these conventional mappings for retransmission, either the transmitter maintains the original four layers and is likely to fail to receive the retransmitted data correctly due to poorer channel conditions, or a single codeword is transmitted to the time using only a single layer. However, in the latter case, it is likely that the interleaved and ratematched bits of the HARQ buffer will not fit when fewer layers are available. Thus, in the best case, repetition of rate-matching and interleaving may be required, but in the worst case, the underlying number of information bits does not enter/ fits when fewer layers have to be used, or at least the code rate becomes excessively high. Similar problems arise if one of the HARQ processes is terminated before the other and the channel rank then drops to one.

A solution to this problem according to exemplary embodiments is to provide additional or alternative mappings between codewords and layers that allow a transmitter/transceiver to be able to reduce the number of simultaneously transmitted codewords (or HARQ processes) without being forced to change the number of layers corresponding to any of the remaining codeword(s) (or HARQ process(es). Mappings supporting this capability may be added solely for use in retransmissions, or may also be made available for use by a transmitter on the first data transmission. For example, when considering mappings between codewords and layers as depicted in Figures 4(a)-4(d), the change in rank from four to two transmissions currently forces each codeword to use one layer each. To avoid that problem, one or more additional mappings involving a single codeword can be provided to two (or more) layers for different channel ranges.

One such mapping according to an exemplary embodiment is illustrated in Figure 6(a). In this, for a rank 2 radio channel, a single codeword 700 is mapped to two layers 702 and 704 via S/P unit 706. The resulting layers have their symbols pre-encoded by unit 708 and then are distributed between transmit antennas 710-716. The parameter n which further identifies the codeword 700 in Fig. 6(a) indicates the number of the codeword and is set to one or two, for example, if the mapping of Fig. 6(a) is used by a transmitter to retransmit a codeword 2 that was originally transmitted using the mapping of, say, Fig. 4(d), then n would equal 2. According to another exemplary embodiment, which is illustrated in Fig. 6(b ), a mapping between a single codeword and three layers for a rank 3 radio channel may also or alternatively be provided to a set of mappings between codewords and layers. In it, a codeword 720 is mapped to three different layers 722, 724, and 726 using an S/P unit 728. The resulting three layers are input to the pre-coding unit 730, which pre-encodes the symbols and distributes them. , in this example, between the four transmit antennas 710-716.

In these mappings between codewords and layers according to exemplary embodiments, the pre-coding unit 708, 730 may be responsible for the ordering of layers 702 and 704 or 722, 724 and 726, respectively. Therefore, in figures 6(a) and 6(b) there is no explicit reference to different orderings of layers although it would be easy to do so. Furthermore, it will be apparent that, for retransmissions, the number of codewords may change for any given mapping. The mapping examples illustrated in Figures 6(a) and 6(b) can be used as part of either the mapping sets illustrated in Figures 4(a)-5(d) either individually or together to extend those mapping sets, or they can be used with other mapping sets.

The addition of additional mappings to existing mapping sets may, in turn, impose a need to indicate to the receiver which mapping is being used by a transmitter for a given codeword or data block. In LTE, the receiver ( UE) will, for example, rely on channel measurements, which recommend a certain transmission range and pre-coder to the eNodeB. For transmission ranges where there is only one possible mapping, the receiver's recommendation of a transmission range implicitly determines the mapping between codewords and layers. An alternative is for the UE to explicitly recommend a mapping between codewords and layers from which the transmission range is implicitly derived, eg by signaling such a recommendation to the eNodeB. The eNodeB can choose to follow the transmission range recommendation or override it. In any case, the eNodeB can generate a signal, in the downlink towards the user equipment, indicating which mapping/transmission range is used to transmit to it. There are several alternatives that can be used to generate signal(s) indicating which specific mapping to use and, in particular, how to add the extended mappings. The signaling should preferably be considered together with, for example, the pre-coding index signaling and in LTE it would probably be included in the Physical Downlink Control Channel (PDCCH). In any case, an exemplary way of adding support for additional mappings is to let the size field of the PDCCH transport format, which describes the number of bits of information in a codeword, be set to zero when that codeword it must remain unused so that the corresponding layers are not transmitted.

As mentioned above, the transmission processing techniques described in this document can be used for various communication systems such as Code Division Multiple Access (CDMA) systems, time division multiple access systems ( TDMA - Time Division Multiple Access), multiple access systems by frequency division ( FDMA - Frequency Division Multiple Access), orthogonal FDMA systems ( OFDMA - Orthogonal FDMA), single carrier FDMA systems (SC FDMA), etc. The transmitter/transceiver may, for example, be arranged at a radio base station, at a NodeB, at an eNodeB, or the like, to transmit information signals on a downlink radio channel. Alternatively, the transmitter may, for example, be arranged in a mobile unit, terminal device, user equipment, or the like, to transmit information signals on an uplink radio channel. Regardless of the particular type of communication system in which these exemplary embodiments are presented, the transmission device will typically include the components generally illustrated in Figure 7.

In this, the transmitter includes a plurality of physical transmit antennas 802, which in this example are four, but more or less than four transmit antennas may be used. Physical transmit antennas 802 are connected to a processor 806 via transmit chain elements 804 which may include one or more filters, power amplifiers, and the like, as will be appreciated by those skilled in the art. A processor(s) 806, along with a memory device(s) 808 (and possibly other devices not shown) may function to perform the transmission processes discussed above with respect to Figures 1-3, for example, as software stored on it, additional hardware, or some combination of software and hardware. Thus, the mapping functionality between codewords and layers described above may, for example, be performed in software by executing computer-readable instructions from memory device 808 to perform, for example, the mappings described above with respect to to Figures 6(a) and 6(b). Therefore, it will be apparent that the exemplary embodiments also relate to software, eg, program code or instructions that are stored on a computer-readable medium and that, when read by a computer, processor, or the like, they perform certain steps associated with the transmission of information signals whose HARQ codewords are mapped to the layers in the manner described above. Examples of such steps are illustrated in the flow charts in Figures 8 and 9.

Figure 8 illustrates a method of transmitting an information signal, including retransmission of, for example, an erroneously received code word, according to an exemplary embodiment. Here, in step 900, codewords are generated, ie one from each of, for example, two HARQ processes. The codewords are mapped to a first plurality of layers corresponding to a first transmission range, i.e., the number of layers equals the transmission range, based on, for example, the channel range perceived by the transmitter at the time of the first transmission of this data, at step 902 to generate an information signal. The information signal is then transmitted over the radio channel in step 904. Subsequently, in step 906, one of the HARQ processes is commanded to retransmit, and a corresponding codeword is produced and retransmitted, for example, due to to the erroneous reception by a receiver of the first transmission of a coded word associated with the HARQ process to which the retransmission was ordered. The code word to be retransmitted is mapped to a second plurality of layers and transmitted with a second transmission range, eg, associated with the channel conditions perceived by the transmitter at the time of retransmission.

Figure 9 illustrates a method of transmitting an information signal, which may or may not include retransmission, according to an exemplary embodiment. Therein, at step 1000, a codeword of a HARQ process is generated. This codeword is mapped, in step 1002, to a plurality of layers corresponding to a transmission range, for example, based on a channel range of the radio channel, to generate the information signal, where the range transmission range is greater than one and the number of layers is equal to the transmission range. The resulting information signal is then transmitted in step 1004.

As mentioned above, it is contemplated that receivers of signals processed for transmission as described above will have to consider the mapping between codewords and layers used for transmission in order to decode the received signal. Therefore, an exemplary receiver 1000 for receiving and processing information signals that have been mapped between codewords and layers as described above is illustrated in FIG. 10 . In it, one (or more) receive antennas 1002 receive the information signals that have been mapped between codewords and layers during processing on the transmit side. After passing through one or more receive chain processing elements 1004 (for example, filters, amplifiers, or the like), a processor(s) 1006 will process the received information signals to extract the information contained in the received information signals. themselves, for example, in combination with the processing software stored in a memory device(s) 1008, using its knowledge of the mapping between codewords and layers performed on those information signals.

For example, as shown in the flowchart of Fig. 11, a method of receiving an information signal that was transmitted using an Automatic Hybrid Repeat Request ( HARQ) codeword may include the steps of receiving the information signal 1100 and determining a first mapping between the codewords and a first plurality of layers that was used to generate the information signal having a first transmission range (step 1102). Using this mapping knowledge, the receiver can then decode the received information in step 1104. A retransmission of at least part of the information signal then occurs in step 1106 in a second transmission range. The receiver can then determine a second mapping between at least one of the codewords and a second plurality of layers (step 1108) and use that knowledge to decode the retransmitted information signal in step 1110.

The foregoing description of exemplary embodiments provides illustration and description, but is not intended to be exhaustive or to limit the invention to the particular form described. Modifications and variations are possible in light of the above teachings or may be acquired by practice of the invention. The following claims define the scope of the invention.

Claims (16)

1. A method of transmitting an information signal on a radio channel using HARQ Hybrid Automatic Repeat Request codewords, the method comprising: generate at least two codewords (900), one for each HARQ process available for simultaneous transmission; mapping using a codeword-to-layer mapping said at least two codewords (902) to a first number of layers to generate said information signal having a first transmission range equal to the first number of layers, wherein at least one of said at least two coded words is mapped to at least two layers and comprises a block of information bits; initially transmitting (904) said information signal on said radio channel; receiving a request to resend the information contained in at least one of the plurality of codewords; retransmit (906) the block of information bits comprised in said one of the codewords that has been mapped to at least two layers, with a second transmission range on said radio channel, wherein the second transmission range is at least two, and wherein the second transmission range is reduced compared to the first transmission range, using one of said HARQ processes, retransmission (906) comprising the steps of: generating a retransmission codeword based on the information bit block; mapping using a codeword-to-layer mapping said retransmission codeword to a second number of layers; Y transmitting said retransmission codeword in said second transmission range equal to the second number of layers, wherein the second number of layers is the same number of layers to which said one of the codewords has been mapped in the initial transmission (904 ), and in which the layers are streams of symbols that are input in parallel to a pre-encoder, wherein mapping of codeword to layer to be used is signaled by setting equal to zero the transport format size field corresponding to the codeword that is to remain unused. 2. The method of claim 1, wherein said at least one of the plurality of codewords is mapped to two or three layers. 3. The method of claim 1 or 2, wherein: in the initial transmission, the transmission rank is four and two codewords are transmitted; and in the relay transmission, the transmission rank is less than four. The method of claim 3, wherein the transmission range for the retransmission transmission is two, and the retransmission codeword is mapped to two layers. 5. The method of claim 3 or 4, comprising receiving a request to resend the information contained in only one of the two codewords. The method of any one of claims 1 to 5, further comprising signaling the codeword-to-use-layer mapping to a receiver. 7. The method of any one of claims 1 to 6, wherein the layers are streams of symbols that are input in parallel to a pre-encoder. The method of any one of claims 1 to 7, wherein the number of layers is the same number of layers to which the codeword has been mapped in the initial transmission. 9. A transmitter (800) for transmitting an information signal on a radio channel using HARQ Hybrid Automatic Repeat Request codewords, the transmitter comprising: at least one processor (806) adapted to generate at least two codewords, one for each HARQ process available for simultaneous transmission, wherein the processor is adapted to map using codeword-to-layer mapping said at least two codewords to a first number of layers to generate said information signal having a first transmission range equal to the first number of layers, in wherein at least one of said at least two codewords is mapped to at least two layers and comprises a block of information bits; and at least one memory, the memory comprising instructions which, when executed by the processor, cause the transmitter initially transmit said information signal; receive a request to resend the information contained in at least one of the plurality of codewords; retransmit the information bit block comprised in said one of the codewords that has been mapped to at least two layers, with a second transmission range on said radio channel, wherein the second transmission range is at least two, and wherein the second transmission rate is reduced compared to the first transmission rate, using one of said HARQ processes, the retransmission comprising the steps of: generating a retransmission codeword based on the information bit block; mapping using a codeword-to-layer mapping said retransmission codeword to a second number of layers; transmitting said retransmission codeword in said second transmission range equal to the second number of layers, wherein the second number of layers is the same number of layers to which said one of the codewords has been mapped in the initial transmission (904 ), and in which the layers are streams of symbols that are input in parallel to a pre-encoder, wherein mapping of codeword to layer to be used is signaled by setting equal to zero the transport format size field corresponding to the codeword that is to remain unused. 10. The transmitter of claim 9, wherein the at least one of the plurality of codewords is mapped to two or more layers. 11. The transmitter of claim 9 or 10, wherein: in the initial transmission, the transmission range is four and two codewords are transmitted; and in the relay transmission, the transmission rank is less than four. 12. The transmitter of claim 11, wherein the transmission range for the retransmission transmission is two, and the retransmission codeword is mapped to two layers. 13. The transmitter of claim 11 or 12, further comprising instructions that, when executed by the processor, cause the transmitter to receive a request to resend the information contained in only one of the two codewords. The transmitter of any one of claims 9 to 13, further comprising instructions that, when executed by the processor, cause the transmitter to signal the codeword-to-use-layer mapping to a receiver. 15. The transmitter of any one of claims 9 to 14, wherein the layers are streams of symbols that are input in parallel to a pre-encoder. 16. The transmitter of any one of claims 9 to 15, wherein the number of layers is the same number of layers to which the codeword was mapped in the first transmission.